title: Phencyclidine false positive induced by lamotrigine (Lamictal®) on a rapid urine toxicology screen.
abstract: BACKGROUND
  This report describes two cases with unexplained positive results for phencyclidine (PCP).
  
  
  OBJECTIVE
  This case will correlate lamotrigine (Lamictal®) use with false-positive results for PCP on a rapid urine toxicology screen.
  
  
  METHODS
  Case 1: A 62-year-old male arrived to the emergency department in extreme psychosis. All positive results on the urine drug screen could be accounted for except PCP. A comprehensive drug screen was performed to confirm PCP use, but returned negative. PCP was ruled out as the causative agent. The reason for the PCP false positive remained unknown. Case 2: A 49-year-old female presented to the ED with a history of seizures and depression. Despite positive PCP results on a rapid urine drug screen, PCP use was ruled out due to patient presentation and comprehensive history.
  
  
  RESULTS
  The differential diagnosis in case 1 included PCP abuse until PCP was ruled out by a comprehensive drug screen. A literature search failed to explain a reason for false-positive results. The patient in case 2 was not psychotic, but returned a positive urinalysis result for PCP. Case 2's presentation combined with a comprehensive history at the facility ruled out PCP use. Both patients were taking the anti-seizure medication lamotrigine with nothing else in common.
  
  
  CONCLUSIONS
  Lamotrigine has the potential to cause false-positive results for PCP on the Bio-Rad TOX/See urine toxicology screen.
authors.affiliation: Emergency Department, Baptist Medical Center Downtown, 800 Prudential Drive, Jacksonville, FL 32207 USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Geraci
authors.forename: James
authors.initials: J
authors.lastname: Peele
authors.forename: Stacey L
authors.initials: SL
authors.lastname: McCoy
authors.forename: Brad
authors.initials: B
authors.lastname: Elias